Here's a new thesis about Mozart's death: that he died of too little sunlight, and thus, too little vitamin D. Here's a 2007 post meditating on the nocturnal life of composers:
The working habits of the wild composer are as diverse as the music. Some, especially those pedagogically engaged, are early risers and writers, often finding their muse well before a proper breakfast has been hunted and/or gathered. Others keep strict bankers' hours and, when fortunate, their muses are equally punctual. But concerts and theatrical events in the western tradition are generally evening events (any doubt? is there anything worse than a concert in Darmstadt on a Summer's afternoon?) and many composers, like their concertizing colleagues, shift their timeclocks appropriately, four or more hours forward. After a concert, often the first item of discussion among the empty stomached participants is locating a local restaurant with late hours. (The comedian Don Novello once did a TV promo for the San Francisco Art Institute, identifying the artist's late waking hour as an advantage over other professions, like medicine or the law). None other than J.S. Bach, during his mature years, would adjourn each evening to compose, alone but for the bottle of Weinbrand which he emptied each night. My evidence is only personal and anecdotal, but I am convinced that the ratio of the truly nocturnal to the more-or-less diurnal among composers is higher than that among the population at large. I count myself in that number.
Whatever the immediate causes -- refuge from a necessary day job, or the business of family life, insomnia, or plain choice, working at night has its advantages. You are composing at an edge of consciousness, between waking and dreaming, often the ideal state of mind for imagining a new music. It is the more quiet half of the day, and the less social, less interrupted by the rhythms and counter-rhythms of the modern day. It is a time of day in which natural sounds tend to dominate the mechanical. Growing up in the overgrown desert of Southern California, the night was charged by the increase in moisture in the air and sounds traveled differently at night, with choruses of crickets joined by the doppler-shifted moans of passing AT&SF trains or speeding cars on Route 66 with all the green lights lit. But I digress.
Whether rising early or late, the composers I've known tend to be nappers. Some have mastered the art of napping during the works of unfavored colleagues. Most are deep sleepers, indeed dreamers. Me, I'm far too evil to rest. Should you encounter a wild composer, he or she may very well want to follow you home. This is not always advised, but if you do choose the companionship of a composer, feed them well (or let him or her feed you well, as we are often good in the kitchen), find them a comfortable place to nap, and never introduce her or him to a loan officer. In return, your composer, when correctly domesticated, will provide you with hours of entertainment and perhaps even a bit of affection in return.